Optical switch and optical add/drop multiplexer using the same

ABSTRACT

An optical switch easy to adjust optical parts without using a catoptric system and an optical add/drop multiplexer using the optical switch are provided. Between an input light outputting collimator device 20 and an output light inputting collimator device 21 provided to face each other at a predetermined spaced interval, a drop light inputting collimator device 22 and an add light outputting collimator device 23 fixed and held on a movable holding member 24 a in common are moved forward and retreated, and thereby a switching is conducted.

This is a Divisional of application Ser. No. 10/515,378, filed Feb. 28,2005, which in turn is a National Stage Application of PCT/JP03/06386,filed May 22, 2003. The entire disclosure of the prior applications arehereby incorporated by reference herein their entirety.

BACKGROUND

1. Technical Field

The present invention relates to an optical switch used for change of anoptical path of a signal light or the like and an optical add/dropmultiplexer using the optical switch in a field of optical communicationor the like.

2. Background Art

In recent years, a development of a wavelength-division multiplexingsystem has been advancing in an optical communication, and recently, anoptical communication system has been drawing attention, which has anadd/drop (Add/Drop Multiplexer: ADM) function to sort out and utilizeonly a signal light of a specific wavelength from among plural signallights at a repeater station being provided in a middle of an opticaltransmission line, or to add and transmit other signals from thisrepeater station into the optical transmission line, in addition toperform a transmission/reception between two stations. A devicedisclosed in Japanese Patent Laid-open No. 2000-183816 is known as anoptical add/drop multiplexer utilized in such an optical communicationsystem.

The optical add/drop multiplexer includes an optical demultiplexer whichreceives a multiple wavelength light from the optical transmission lineand demultiplexes it into signal lights of respective wavelengths, andan optical multiplexer which remultiplexes and transmits the signallights demultiplexed into the respective wavelengths to the opticaltransmission line, and has two by two channel optical switches forswitching optical paths of the signal lights to either (a) or (b)described below corresponding to the respective signal lightsdemultiplexed by the optical demultiplexer, between the opticaldemultiplexer and the optical multiplexer.

(a) transmits the signal lights straight to the optical transmissionline without dropping them to the repeater station; and

(b) drops the signal lights to the repeater station and simultaneouslyadds the signal lights transmitted from the repeater station to theoptical, transmission line.

The multiple wavelength light inputted to such an optical add/dropmultiplexer is firstly demultiplexed into the signal lights of therespective wavelengths by the optical demultiplexer. Further, theoptical paths of the respective signal lights are selected to be eitherthe aforementioned (a) or (b), by the optical switches provided inaccordance with the signal lights of the respective wavelengths, andonly the signal lights of the wavelengths used at the repeater stationare dropped at the repeater station. The dropped signal lights areutilized at the repeater station, and the signal lights transmitted fromthe repeater station to be added to the optical transmission line aresent to the optical multiplexer via the optical switches. The signallights of the respective wavelengths are remultiplexed at the opticalmultiplexer and sent to the optical transmission line as-the multiplewavelength light.

As the two by two channel optical switch used for the optical add/dropmultiplexer, switches using prisms are conventionally known as disclosedin Japanese Patent Laid-open No. 2000-2843 and U.S. Pat. No. 5,436,986.

FIG. 12 shows a conventional optical switch 100 of the two by twochannel using prisms. In the optical switch 100, an inputting opticalfiber collimator 10 which inputs signals demultiplexed by the opticaldemultiplexer, and an outputting optical fiber collimator 11 which sendsthe signal lights to the optical multiplexer for multiplexing areprovided to face each other at a predetermined spaced interval. On theother hand, a dropping optical fiber collimator 12 which drops thesignal lights to a repeater station is disposed adjacent to theinputting optical fiber collimator 10, and an adding optical fibercollimator 13 which adds the signal lights from the repeater station isdisposed adjacent to the outputting optical fiber collimator 11, and thedropping optical fiber collimator 12 and the adding optical fibercollimator 13 are also disposed to face each other at a predeterminedspaced interval.

Furthermore, two right-angle prisms 14 and 15 are movably disposed in apredetermined spaced intervals formed between the facing two pairs ofcollimators. A switching of the above-described optical paths (a) or (b)is conducted by a movement of the prisms. In other words, when theprisms are placed at the positions shown by solid lines in the drawing,a light outputted from the inputting optical fiber collimator 10 isreflected by these prisms and inputted to the dropping optical fibercollimator 12, and a light added from the adding optical fibercollimator 13 is similarly reflected by these prisms and inputted to theoutputting optical fiber collimator 11, and thereby, the optical path(b) is formed.

On the other hand, when the prisms are placed at retreat positions shownby dotted lines in the drawing, the signal light outputted from theinputting optical fiber collimator 10 is inputted to the outputtingoptical fiber collimator 11, and thereby the optical path (a) is formed.

Besides, as a similar two by two channel optical switch, a switch usinga reflector instead of the prisms is generally known (for example, referto Japanese Patent Laid-open No. 2001-133705). It is a switch whichreflects an input light with the reflector by disposing the reflectormovably between the outputting optical fiber collimator and theinputting optical fiber collimator so as to switch the optical path.

However, the aforementioned optical switches using the prisms or thereflector had problems described below. Conventional optical switchesuse a catoptric system, and a loss of lights at the time of reflectionis inevitable when drop of the signal lights to the repeater station andaddition of the signal light from the repeater station are conducted.

Besides, at the time of reflection, a light is reflected in anorthogonal direction by the prisms or the reflector, and a phenomenon(PDL: Polarization Dependence Loss) in which a loss is changed dependingon a polarized wave of the light is inevitable when the light is thusreflected in an oblique direction. When such a PDL occurs, a bit errorrate in the optical communication becomes high, and as a result, thereis a problem of deterioration in the quality of the opticalcommunication.

Furthermore, in the conventional optical switches, it is required toadjust the prisms or the reflector to the optical fiber collimators withhigh precision in addition to position adjustments between the opticalfiber collimators. Especially, when the catoptric system such as theprisms, the reflector, or the like is used, axis deviation of thereflected light becomes large due to an angular misalignment of theprisms or a mirror, and therefore, there is a problem that the alignmentof optical parts is difficult.

The present invention is made in order to solve the aforementionedproblems, and it is an object of the present invention to provide anoptical switch which does not use the catoptric system and easy foralignment. Furthermore, it is an object of the present invention toprovide an optical add/drop multiplexer using this optical switch.

DISCLOSURE OF THE INVENTION

In order to solve the above-mentioned problems, a first means is:

An optical switch, being provided in a middle of an optical transmissionline, which switches a light sent through this optical transmission lineeither to be transmitted straightly or to be sorted outside andsimultaneously the light from outside is introduced and sent to theoptical transmission line, the optical switch including:

an input light outputting collimator device which collimates and outputsa light sent through the optical transmission line;

an output light inputting collimator device which inputs the collimatedlight outputted from the input light outputting collimator device at aposition away for a predetermined distance and introduces and sends thecollimated light to the optical transmission line; and

an optical switching portion retreatably disposed between the inputlight outputting collimator device and the output light inputtingcollimator device, wherein

the optical switching portion includes a drop light inputting collimatordevice which inputs the collimated light outputted from the input lightoutputting collimator device, introduces the collimated light to adropping transmission line, and sends the collimated light to outsidewhen the optical switching portion is disposed between the input lightoutputting collimator device and the output light inputting collimatordevice, and an add light outputting collimator device which collimatesand outputs a light sent from outside through an adding transmissionline, and the collimated light is inputted to the output light inputtingcollimator device, and introduces the collimated light to an outputtingtransmission line.

A second means is:

the optical switch according to the first means, wherein

the input light outputting collimator device, the output light inputtingcollimator device, the drop light inputting collimator device, and theadd light outputting collimator device are optical fiber collimatordevices.

A third means is:

the optical switch according to the first or the second means, wherein

the optical switching portion forms a V-shaped groove on a movableholding member retreatably disposed between the input light outputtingcollimator device and the output light inputting collimator device, andfixes to hold the drop light inputting collimator device and the addlight outputting collimator device on the V-shaped groove.

A fourth means is:

an optical add/drop multiplexer, includes:

an optical demultiplexer which demultiplexes a multiple wavelength lighttransmitted from an optical transmission line into signal lights ofrespective wavelengths;

an optical switch, being provided in accordance with the respectivesignal lights of the respective wavelengths demultiplexed at the opticaldemultiplexer, which switches optical paths of the signal lights of therespective wavelengths to either

(a) a case of transmitting the Menial lights straight to the opticaltransmission line without dropping them to a repeater station, or

(b) a case of dropping the signal lights to the repeater station andsimultaneously adding the signal lights sent from the repeater stationto the optical transmission line; and

an optical multiplexer which multiplexes the signal lights added fromthe repeater station and the signal lights transmitted without beingdropped to the repeater station in the optical switch to make a multiplewavelength light, wherein

the optical switch according to any one of the first means to the thirdmeans is used as the optical switch.

SUMMARY

As explained above, according to the present invention, an opticalswitch can be obtained, in which an optical communication of highquality with small loss is possible because it is not necessary to use acatoptric system, and an alignment thereof is easy. Besides, an opticaladd/drop multiplexer capable of the optical communication of highquality using the optical switch can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a structure of an optical switch 200according to the present embodiment;

FIG. 2 is a perspective view showing an example of an optical switchingportion 24;

FIG. 3 is a view showing a concrete structure of an input lightoutputting collimator device 20;

FIG. 4 is a perspective view showing a concrete structure of an opticalswitch according to an embodiment of the present invention;

FIG. 5 is a plan view showing a concrete structure of the optical switchaccording to the embodiment of the present invention;

FIG. 6 is a perspective view showing a transformed example of theoptical switch shown in FIG. 5;

FIG. 7 is a perspective view showing another concrete structure of theoptical switch according to the embodiment of the present invention;

FIG. 8 is a plan view of the optical switch shown in FIG. 7;

FIG. 9 is an explanatory view of the optical switch shown in FIG. 7 andFIG. 8;

FIG. 10 is an explanatory view of the optical switch shown in FIG. 7 andFIG. 8;

FIG. 11 is a view showing a structure of an optical add/drop multiplexeraccording to the embodiment of the present invention; and

FIG. 12 is a view showing a conventional two by two channel opticalswitch.

10 inputting optical fiber collimator

11 outputting optical fiber collimator

12 dropping optical fiber collimator

13 adding optical fiber collimator

20 input light outputting collimator device

21 output light inputting collimator device

22 drop light inputting collimator device

23 add light outputting collimator device

14,15 prism

24 optical switching portion

24 b V-shaped groove

31,32 optical transmission line

33 optical demultiplexer

34 optical multiplexer

36 transmitter

37 receiver

100,200 optical switch

300 optical add/drop multiplexer

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a plan view showing a structure of an optical switch 200according to the present embodiment; FIG. 2 is a perspective viewshowing an example of an optical switching portion 24; FIG. 3 is a viewshowing a concrete structure of an input light outputting collimatordevice 20; FIG. 4 is a perspective view showing a concrete structure ofan optical switch according to an embodiment of the present invention;FIG. 5 is a plan view showing a concrete structure of the optical switchaccording to the embodiment of the present invention; FIG. 6 is aperspective view showing a transformed example of the optical switchshown in FIG. 5; FIG. 7 is a perspective view showing another concretestructure of the optical switch according to the embodiment of thepresent invention; FIG. 8 is a plan view of the optical switch shown inFIG. 7; FIG. 9 and FIG. 10 are explanatory views of the optical switchshown in FIG. 7 and FIG. 8; and FIG. 11 a view showing a structure of anoptical add/drop multiplexer according to the embodiment of the presentinvention. The optical switch and the optical add/drop multiplexeraccording to the embodiment will be explained hereinafter with referenceto the drawings.

As shown in FIG. 1, the optical switch according to the presentembodiment includes an input light outputting collimator device 20 whichcollimates and outputs a light sent through an upstream side opticaltransmission line 20 a constituted by an optical fiber or the like, andan output light inputting collimator device 21 which inputs thecollimated light outputted from the input light outputting collimatordevice 20 at a position away for a predetermined distance and introducesand sends the collimated light to a downstream side optical transmissionline 21 a constituted by the optical fiber or the like, and furthermore,an optical switching portion 24 is retreatably disposed between theinput light outputting collimator device 20 and the output lightinputting collimator device 21.

The input light outputting collimator device 20 and the output lightinputting collimator device 21 are disposed so that their output endface and input end face are opposed with each other having an opticalaxis in common with each other. Therefore, when the optical switchingportion 24 is retreated from therebetween, the light outputted from theinput light outputting collimator device 20 is straightly inputted tothe output light inputting collimator device 21 to be transmitted.

The optical switching portion 24 is so structured that a drop lightinputting collimator device 22 and an add light outputting collimatordevice 23 are mounted on a movable holding member 24 a. When the opticalswitching portion 24 is disposed between the input light outputtingcollimator device 20 and the output light inputting collimator device21, the drop light inputting collimator device 22 inputs the collimatedlight outputted from the input light outputting collimator device 20 andintroduces the collimated light to a dropping transmission line 22 a, tosend the light to the outside. Besides, when the optical switchingportion 24 is disposed between the input light outputting collimatordevice 20 and the output light inputting collimator device 21, the addlight outputting collimator device 23 collimates and outputs a lightsent from outside through an adding transmission line 23 a, and inputsthe collimated light to the output light inputting collimator device 21,to introduces to the downstream side optical transmission line 21 a.

Here, optical fiber collimators are used for the input light outputtingcollimator device 20, the output light inputting collimator device 21,the drop light inputting collimator device 22, and the add lightoutputting collimator device 23. The optical fiber collimator has, forexample, an optical output end or an optical input end of the opticalfiber being an optical transmission line having an optical axis incommon, and a collimate lens which makes the light outputted or inputtedthrough the optical output end or the optical input end to be acollimated light or a convergence beam, in a cylindrical tube polishedwith high precision. A convex lens, an aspherical lens, a gradedrefractive index rod lens, and the like can be used for the collimatelens. A lens and a fiber may be held and fixed with an adhesive, or thelens may be fused and fixed to the fiber in a common glass tube or astainless tube. The adhesive does not exist between the lens and thefiber in either case, and they are optically free and can correspond tohigh power.

FIG. 3 is a view showing a concrete structure of the input lightoutputting collimator device 20. In the input light outputtingcollimator device 20, an optical output end of the optical fiber 20 a isfused and fixed to an aspherical lens 200 c, and a output end portion ofthe optical fiber 20 a is covered with a holding portion 20 b and fixedwith an adhesive in a stainless tube 200 a.

Further, as another example of the optical fiber collimator, such anoptical fiber collimator may be used that an optical fiber inserted to acylindrical holding portion having substantially the same diameter as agradient index lens being a collimate lens, and an oblique end face of arod type gradient index lens of which end face is also formed obliquely,are faced with each other, and inserted to a cylindrical member made ofa glass tube, stainless steel, or the like, and fined with an adhesive.Besides, a collimator using a fiber in which a coreless fiber having aspecific length exists at the optical output end or the optical inputend can be used. This collimator has such a characteristic that anoutput and/or input angle is small, and that a reflection loss is small.A collimator of this kind is commercially available, for example, fromLightpath Technologies, Inc (1.6 mm φ, 7 mm long).

The optical switching portion 24 is, for example, as shown in FIG. 2, sostructured that, in a V-shaped groove 24 b formed on the movable holdingmember 24 a, the drop light inputting collimator device 22 and the addlight outputting collimator device 23 are disposed so that each end faceof the optical input or output faces outward, and they are fixed andheld to have an optical axis in common. The movable holding member 24 ais movably formed at the spaced interval formed between the input lightoutputting collimator device 20 and the output light inputtingcollimator device 21 by a later-described drive mechanism, so that thefollowing position of (A) and (B) can be switched.

(A) A first position (a position shown by a solid line in the drawing,hereinafter referred to as an add/drop position) so disposed that theadd light outputting collimator device 23 and the drop light inputtingcollimator device 22 are disposed at a spaced interval formed betweenthe input light outputting collimator device 20 and the output lightinputting collimator device 21 in order to make such a dispositionrelationship that the input light outputting collimator device 20 andthe drop light inputting collimator device 22 fixed on the movableholding member 24 a are disposed to face each other, and that the addlight outputting collimator device 23 fixed on the movable holdingmember 24 a and the output light inputting collimator device 21 aredisposed to face each other.

(B) A second position (a position shown by a dotted line in the drawing,hereinafter referred to as a retreat position) that the add lightoutputting collimator device 23 and the drop light inputting collimatordevice 22 are retreated out of the spaced interval formed between theinput light outputting collimator device 20 and the output lightinputting collimator device 21 so that the light outputted from theinput light outputting collimator device 20 is not obstructed to inputto the output light inputting collimator device 21.

In the case of the (A), the light outputted from the input lightoutputting collimator device 20 is inputted to the drop light inputtingcollimator device 22, and simultaneously the light outputted from theadd light outputting collimator device 23 is inputted to the outputlight inputting collimator device 21. In other words, it becomes a state(hereinafter referred to as a state (ii)) that the light sent from theupstream side optical transmission line 20 a is introduced to thedropping transmission line 22 a, and that the light sent from the addingtransmission line 23 a is introduced to the downstream side opticaltransmission line 21 a.

In the case of the (B), the light outputted from the input lightoutputting collimator device 20 is straightly inputted to the outputlight inputting collimator device 21. In other words, it becomes a state(hereinafter referred to as a state (i)) that the light transmittedthrough the upstream side optical transmission line 20 a is straightlyintroduced to the downstream side optical transmission line 21 a.

As described above, either the add/drop position of the (A) or theretreat position of the (B) is selected as a position of the movableholding member 24 a, and thereby, a switching of the optical path of thelight sent through the upstream side optical transmission line 20 a andoutputted from the input light outputting collimator device 20 isconducted.

Besides, as explained above, the retreat position of the movable holdingmember 24 a may be the position which does not obstruct the optical pathfrom the input light outputting collimator device 20 to the output lightinputting collimator device 21. However, it is preferable if the opticalaxis of the add light outputting collimator device 23 and the drop lightinputting collimator device 22 at the retreat position is placed to bein parallel with the optical axis of the input light outputtingcollimator device 20 and the output light inputting collimator device21, and also, input/output ends of the input light outputting collimatordevice 20 and the drop light inputting collimator device 22 is placed toface each other, and input/output ends of the output light inputtingcollimator device 21 and the add light outputting collimator device 23is placed to face each other, switching can be conducted by a simpleparallel movement of the movable holding member 24 a. When such theparallel movement is performed, any movement in a perpendiculardirection (a vertical movement), in a parallel direction (a horizontalmovement), and in a rotational direction is possible, relative to asubstrate face of the movable holding member 24 a.

In the aforementioned example, the drop light inputting collimatordevice 22 and the add light outputting collimator device 23 are fixed onthe V-shaped groove 24 b of the movable holding member 24 a, however, ifthe input light outputting collimator device 20 and the output lightinputting collimator device 21 are also fixed on a V-shaped groovehaving an axis of a groove in common, optical axis adjustment thereofcan be further facilitated. Consequently, the add light outputtingcollimator device 23 and the drop light inputting collimator device 22can be set or out of the predetermined position within the predeterminedspaced interval formed between the input light outputting collimatordevice 20 and the output light inputting collimator device 21, by justmoving and adjusting the position of the movable holding member 24 a,and the switching, between the above-stated state (i) and the state (ii)becomes possible.

The movable holding member 24 a can take any shape and be made of anymaterial as long as it fixes the add light outputting collimator device23 and the drop light inputting collimator device 22 in a predeterminedpositional relationship, but use of a substrate-type materialfacilitates its handling. As a material thereof, a metal such as glassor aluminum, silicon, and resin, can be used. Besides, as describedabove, the movable holding member 24 a has the V-shaped groove, andthereby, a position adjustment of the add light outputting collimatordevice 23 and the drop light inputting collimator device 22 fixedthereon becomes easy. This V-shaped groove can be formed by a cuttingmachining of a substrate, or by copying a shape of a die by way of apress forming if the substrate is made of glass.

It should be noted that UV cure adhesive, a heat curing adhesive,solder, welding, or the like can be appropriately used to fix parts.

As explained above, the optical switch according to the presentembodiment conducts switching by moving the movable holding member 24 ato move the drop light inputting collimator device 22 and the add lightoutputting collimator device 23 fixed on the movable holding member 24a, and a catoptric system is not used at all. Consequently, the problemsof the loss due to reflection and the PDL do not occur at all. Further,the number of the parts can be reduced because a prism or a reflector isnot necessary, which allows to reduce the cost. Furthermore, onlyposition adjustment between the respective optical fiber collimators isrequired, and use of only linear disposition is possible, allowingextremely easy position adjustment between the parts.

Next, a concrete structure of the optical switch according to theembodiment of the present invention will be explained with reference toFIG. 4 and FIG. 5. In these drawings, a numeral 2 represents asubstantially U-shaped base. The base 2 has two mounting plate portions2 a and 2 b provided to face each other, and the input light outputtingcollimator device 20 and the output light inputting collimator device 21are fixed therethrough. A substantially U-shaped movable table 2 cmovably disposed is provided in the base 2. The add light outputtingcollimator device 23 and the drop light inputting collimator device 22are attached to the movable table 2 c having the optical axis in common,and thereby, the optical switching portion 24 is configured. The movabletable 2 c is fixed on a slider 2 e slidably mounted on a rail 2 d. Therail 2 d is provided so that the slider 2 e is movable in an orthogonaldirection to the optical axis of the input light outputting collimatordevice 20 and the output light inputting collimator device 21. Themovable range of the slider 2 e is controlled by stoppers 2 g and 2 f.The slider 2 e can be moved by driving a drive shaft 2 h, which isinserted and fixed in the movable table 2 c, with a linear actuator 2 i.Consequently, the optical switching portion 24 can be disposedretreatably between the input light outputting collimator device 20 andthe output light inputting collimator device 21.

Incidentally, as shown in FIG. 6, a movable table 2 j to which the droplight inputting collimator device 22 and the add light outputtingcollimator device 23 are disposed and fixed on the V-shaped groove canbe used, instead of the substantially U-shaped movable table 2 c.

Next, another concrete example of the optical switch according to theembodiment of the present invention will be explained with reference toFIG. 7 to FIG. 10. In this example, the drop light inputting collimatordevice 22 and the add light outputting collimator device 23 arerespectively inserted to fix through mounting holes 2 k 1 at tipportions of two lever-shaped collimator holders 2 k whose base endportions are attached to a rotation shaft 2 m. The collimator holders 2k are rotationally driven by using the rotation shaft 2 m as a rotationshaft, and thereby, the optical switching portion 24 is retreatablydisposed between the input light outputting collimator device 20 and theoutput light inputting collimator device 21 respectively fixed throughfacing mounting plate portions of the substantially U-shaped base 2.

The rotation shaft 2 m is rotationally supported by shaft receivingmembers 2 n by disposing both end portions thereof in V-shaped shaftreceiving portions of two shaft receiving members 2 n, and by fixingmetal strips 2 p by screws 2 q. The control of the rotation range isconducted by a substantially dogleg-shaped stopper 21 fixed through acenter portion of the rotation shaft 2 m. Rotation drive is conducted byinserting a drive pin 2 r 1 of a solenoid 2 r in cutout portions 21E2provided on upper portions of the base end portions of the collimatorholders 2 k, and by driving the drive pin 2 r 1 in a substantiallyhorizontal direction. In other words, as shown in FIG. 10, when thedrive pin 2 r 1 is moved horizontally in the drawing, the collimatorholder 2 k rotates by using the rotation shaft 2 m as a center, andthereby, the drop light inputting collimator device 22 and the add lightoutputting collimator device 23 inserted in the tip portion of thecollimator holder 2 k moves vertically. The movable range is controlledby the stopper 21; and therefore, the optical switching portion 24composed of the drop light inputting collimator device 22 and the addlight outputting collimator device 23 can be moved from the retreatposition to the add/drop position with no restriction by appropriatelyselecting a shape of the stopper 21.

Incidentally, as a method for supporting the rotation shaft 2 m,bearings can be used in addition to the holding by the V-shaped groovesprovided on the shaft receiving members 2 n and the metal strips 2 p,which is described above. In this case, circle holes are made on theshaft receiving members 2 n instead of the V-shaped grooves, and twobearings (for example, manufactured by NSK Ltd., outside diameter 4 mm,inside diameter 2 mm) are inserted therein. The rotation shaft isinserted and fixed in the respective through holes so that the stopperis disposed inside and that the collimator holders are disposed outsiderelative to the bearings, and thereby the insertable and retreatableoptical switching portion 24 can be obtained.

Incidentally, as the drive mechanism of the optical switching portion24, a moving mechanism for general use can be appropriately used inaddition to the aforementioned drive mechanism. For example, amicromotor or a linear actuator can be used.

Further, a method for providing a magnetic substance on the movableholding member to move the magnetic substance by a magnetic forcegenerated by a magnet disposed outside can be used. In this case, amovable fixing member itself may be formed by a magnetic substancematerial.

As still another method, there is a method for moving the movable fixingmember between the add/drop position and the retreat position by using aball screw or the like.

Besides, a solenoid is used as the drive mechanism and a magnet is usedas a positioning stopper, of, the like, and thereby, a latching type (aself holding type) optical switch not requiring for constantenergization is made possible, then a generation of chattering can berestrained when the stopper is in contact.

Further, by using damping alloys as a part of the members, thegeneration of chattering is restrained when the stopper is in contactwith a base. For example, the members can be obtained by inserting andfixing the damping alloys (manufactured by Seishin Co., Ltd., 5×5 mm, 1mm in thickness) to the base. As described above, the members may bethus inserted to a base portion being in contact with the stopper, orused as a stopper which positions the movable holding member.

Further, as optical fiber collimators used for the input lightoutputting collimator device 20 and the like, the collimators of whichthe lens, the fiber, and so on, are inserted to a cylindrical membersuch as glass, stainless steel, and fixed with an adhesive are used, andtherefore, the adjustment of the optical axis becomes easy by fixingthem on a V-shaped groove formed on a common positioning member inadvance.

Next, an optical add/drop multiplexer using the optical switch of thepresent embodiment will be explained. FIG. 11 is a schematic viewshowing an optical add/drop multiplexer 300 using the optical switch ofthe present embodiment. The optical add/drop multiplexer 300 of thepresent embodiment has an optical demultiplexer 33 which demultiplexes amultiple wavelength light transmitted from an optical transmission line31 into signal lights of respective wavelengths, and an opticalmultiplexer 34 which multiplexes the signal lights demultiplexed intothe respective wavelengths and then resends the signal light to anoptical transmission line 32, and includes plural two by two channeloptical switches 200 of the present invention therebetween so as tocorrespond to the signal lights of the respective wavelengths.

As described above, the optical switch has a function to select eitherto transmit the demultiplexed signal lights straight to the opticalmultiplexer 34 side (the state (i)) or to drop, the demultiplexed signallights to a receiver 37 at a repeater station and add the signal lightssent from a transmitter 36 at the repeater station to the opticalmultiplexer 34 side (the state (ii)). As the optical demultiplexer 33,any optical demultiplexer is acceptable as long as it has a function todemultiplex the multiple wavelength light into lights of the respectivewavelengths. For example, such a device as disclosed in Japanese PatentLaid-open No. Hei 11-337765 is the one which includes plural wavelengthselection filters which transmit only a light of a specific wavelengthband area and reflect lights of other wavelengths and whichdemultiplexes the multiple wavelength light inputted from the opticaltransmission line 31 into respective wavelengths by sequentially passingthrough the wavelength selection filters having different transmissionwavelengths.

As a wavelength selection filter, a filter in which dielectricmultilayered films are formed on a substrate, an optical fiber gratingin which diffraction grating is formed in an optical fiber, and so on,can be used. As another optical demultiplexer 33, as described inJapanese Patent No. 2599786 an arrayed optical waveguide diffractiongrating which forms plural optical waveguides having different length ofoptical paths on the substrate to demultiplex the multiple wavelengthlight to the respective wavelengths can be used.

Further, as the optical multiplexer 34, the same type as theaforementioned optical demultiplexer can be used. The signal lights ofthe respective wavelengths demultiplexed by the optical demultiplexer 33are introduced by the optical switches 200 of the present inventionprovided in accordance with the respective signal lights, and theoptical path is determined either to be dropped, to the repeater stationor to be transmitted straightly according to a selected status of theoptical switches 200. The lights transmitted straightly are multiplexedto the signal lights of the other wavelengths at the optical multiplexer34. The lights dropped to the repeater station are received by thereceiver 37 of the repeater station and utilized. Further, the signallights sent from the transmitter 36 of the repeater station aremultiplexed with the signal lights of the other wavelengths at theoptical multiplexer 34 via the optical switches 200 and sent to theoptical transmission line 32. The adding/dropping of the multiplewavelength light is conducted as described above.

The optical add/drop multiplexer 300 in the present embodiment uses theoptical switch according to the present invention which does not use acatoptric system, and therefore, it is possible to conduct an opticalcommunication of high quality without having problems of the loss due toreflection and the PLC Besides, the optical switch being used in thepresent invention can reduce the number of parts; moreover, costreduction is possible because position adjustment between the parts isextremely easy, and as a result, a cost reduction of the overall opticaladd/drop multiplexer becomes possible.

1. An optical switch, provided in a middle of an optical transmissionline, for switching between a case when a light sent through the opticaltransmission line is straightly transmitted, and a case when the lightsent through the optical transmission line is transmitted to an outsidelocation and the light from the outside location is introduced to theoptical transmission line, the optical switch comprising: an input lightemitting collimator device which extracts the light sent through theoptical transmission line from an end face of an optical fiber of theoptical transmission line on the upstream side, then, collimates andemits the light thus extracted; an output light receiving collimatordevice which receives the collimated light emitted from the input lightemitting collimator device which is located a predetermined distancetherefrom, and introduces the collimated light to the opticaltransmission line from the end face of the optical fiber of the opticaltransmission line on the downstream side; and a light switching partretractably arranged between the input light emitting collimator deviceand the output light receiving collimator device, wherein the lightswitching part includes: a drop light receiving collimator device whichreceives the collimated light emitted from the input light emittingcollimator device, introduces the collimated light from the end face ofthe optical fiber of a dropping transmission line to the droppingtransmission line, and sends the collimated light to the outsidelocation when the light switching part is arranged between the inputemitting collimator device and the output light receiving collimatordevice; and an add light emitting collimator device which extracts lightsent from an outside location through an adding transmission line fromthe end face of the optical fiber of the adding transmission line,collimates the light, and emits the collimated light to the output lightreceiving collimator device, which introduces the collimated light tothe optical transmission line when the light switching part is arrangedbetween the input light emitting collimator device and the output lightreceiving collimator device.
 2. The optical switch according to claim 1,wherein the input light emitting collimator device, the output lightreceiving collimator device, the drop light receiving collimator deviceand the add light emitting collimator device are optical fibercollimator devices.
 3. The optical switch according to claim 2, whereinsaid optical fiber collimator devices use optical fiber having corelessfiber that exists on an optical emitting end or optical receiving end ofsaid optical fiber, as said optical fiber.
 4. An optical add/dropmultiplexer, comprising: an optical demultiplexer which demultiplexes amultiple wavelength light transmitted from the optical transmission lineinto a plurality of signal lights, wherein each signal light is of arespective wavelength; the optical switch according to claim 1, beingprovided for each signal light of the respective wavelengthdemultiplexed by the optical demultiplexer, which switches an opticalpath of the signal light of the respective wavelength to either (a)straightly transmit the signal light to the optical transmission linewithout dropping the signal light to a repeater station to the opticaltransmission line; and (b) drop the signal light to the repeater stationand add a signal light transmitted from the repeater station to theoptical transmission line; and a light multiplexer which multiplexes thesignal lights, each of which is either straightly transmitted or addedto the optical transmission line, to obtain a multiple wavelength light.5. The optical add/drop multiplexer according to claim 4, wherein theinput light emitting collimator device, the output light receivingcollimator device, the drop light receiving collimator device and theadd light emitting collimator device are optical fiber collimatordevices.
 6. The optical add/drop multiplexer according to claim 5,wherein said optical fiber collimator devices use optical fiber havingcoreless fiber that exists on an optical emitting end or opticalreceiving end of said optical fiber, as said optical fiber.